Many different types of enclosures are filled with a gas for various purposes. Two examples of such enclosures include fluorescent light bulbs and insulated glass units (IGU). IGUs are window structures having two or more panes arranged in parallel with a gas (typically air, a noble gas, or mixtures thereof). Desirable conditions for filling an enclosure with a gas is one that limits gas loss while ensuring a short filling duration and maximum gas content. A low gas loss can be obtained by slow flow rates of filling, but result in long filling duration. Of course, the filling duration can be shortened by increasing the flow rate of filling. However, increasing the flow rate will increase the gas loss. Thus, there is a need for a way to determine an optimum flow rate of filling that limits gas loss but still enables a fast filling and a maximum gas fill (high concentration of the intended gas).
Some conventional IGU filling machines use thermal sensors in order to assess how much of the intended gas has been filled into the enclosure. However, these types of sensor are relatively slow acting which leads to high gas loss. Other conventional filling methods propose the use of a paramagnetic O2 sensor. However this type of sensor has several disadvantages. It is expensive. It restricts the flow of gas and thus requires a vacuum pump to draw small samples out of the IGU being filled. It can also be relatively fragile and sensitive to being bumped. Finally, the paramagnetic O2 sensor can be relatively bulky which requires the sensor to operate “far” (e.g. 10 feet) from the interpane being filled. Because the gas has to flow from the window to the sensor through a dedicated sampling line, there is a delay in sensing the outlet window composition. This time delay translates into gas loss. Thus, there is a need for an improved type of sensor for use in IGU filling machines.
Conventional manual filling processes can generate gas losses ranging from 30% to 200% or more, with an average minimum gas loss of 50%. An additional problem is that these processes often will use the same filling flow rate for all sizes and shapes of IGUs. The gas loss problem has not been a tremendous problem, because most of the current manual filling processes have been developed for cheap filling gases such as Argon. With more expensive gases containing Krypton and/or Xenon, it becomes more important to limit gas losses as much as possible in order to lower the cost of filling.
The patent literature includes some method and systems associated with filling enclosures with gases.
U.S. Pat. No. 5,080,146 (Arasteh) discloses a method for filling insulated glazing units. The method utilizes a vacuum chamber in which the insulated glazing units are placed. The insulated glazing units and vacuum chamber are evacuated simultaneously. The units are then refilled with a low conductance gas such as Krypton while the chamber is simultaneously refilled with air. However, the automated multi-step process is time consuming
U.S. Pat. No. 6,622,456 B2 (Almasy) discloses a method for filling insulating glass units with gases other than air by dispensing cryogenic liquids into the inner space of these units which then evaporates to the gaseous state is disclosed.
U.S. Pat. No. 5,676,736 (Crozel) discloses a two step process for introducing a filling gas (e.g. rare gas mixture) into an enclosure. Initially, the enclosure contains a holding gas (e.g. air). In a first step, a purge gas (e.g. helium), easily extractable from both holding gas and filling gas, is introduced into the enclosure until the holding gas is totally removed from the enclosure. In a second step, the filling gas is injected into the enclosure until a portion or the whole purge gas is removed from the enclosure. The filling gas lost during the second process can then be recycled, thus limiting the manufacturing cost. Optionally, the purge gas can be separated from the holding gas and recycled as well. Proposed methods of separation include permeation (membrane), adsorption, absorption and distillation. Proposed purge gases include Argon, carbon dioxide, Helium and Hydrogen. Proposed filling gases include Argon, Neon, Krypton and Xenon.
In view of the disadvantages posed by conventional methods and systems for filling enclosures (especially IGUs) with a gas, there is a need for an improved method and system which overcomes or does not exhibit these disadvantages.